How to programmatically catch solution upgrade event

Hi,
Im my VS Package i have some logic on "IVsSolutionEvents.OnAfterOpenSolution()".
In case when solution upgrade needed (for instace vs2005 solution -> vs2008), Convert solution wizard opens simultaneously with my logic runs.
I want to catch some sort of this upgrade event and prevent my logic run. (suspend it).

How can I do this? Or how can I may know that opening solution will be converted?

Many thx!
Vasiliy